Electric clock motor control system



June 21, 1955 P. R. coNTANT 2,711,501

ELECTRIC CLOCK MOTOR CONTROL SYSTEM Filed Feb. 2, 1955 M@ ATTORNEYS United States Patent O ELECTRIC CLOCK MOTOR CONTROL SYSTEM Peter R. Contant, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware `Application February 2, 195,3, Serial NO- 334,588

7 Claimi. (Cl. S18- 134) This invention pertains generally to electric clocks and more particularly to a clock of electromagnetic impulse type adapted for automobile installation.

Electromagnetic impulse type clocks are accurate devices if operated underideal conditions of substantially constant applied voltage and a minimum of extraneous vibration. However, it is a well known and recognized fact that the potential of automobile storage batteries liuctuates considerably during vehicle operation. Moreover, automobile clocks are subject to vibrations of substantial magnitude due to adverse road conditions en countered by vehicles. This invention relates to certain improvements in the electromagnetic energizing circuit and in the electromagnet, per se, of a magnetic impulse type clock whereby clocks of this character may be mass produced and require no critical adjustments. Accordingly, among my objects is the provision of an improved energizing circuit for an electromagnetic impulse type clock and the further provision of an improved electro magnet construction ,for enhancing the operation of a magnetic impulse clock.

The aforementioned and other objects are accomplished in the present invention by employing a reactive network including time delay means for timing the energizing cirf cuit, and by providing means for reducing the reluctance of the air gap of the magnetic circuit utilized to sustain balance wheel armature oscillation. Specifically, the improvements relate to a clock of the type disclosed in copending application, Serial No. 604,386, tiled July 1l, 1945, in the names of Peter R. Contant and Raymond H. Sullivan, now Patent No. 2,631,423, wherein a single electromagnet having two sets of poles is used. One set 0f poles, is associated with a timing mechanism including the balance wheel armature which controls and is sustained in oscillation -hy the intermittent energization of the electromagnet, and the other set of poles is associated with a separate driving mechanism including an index armature operably connected to and driving a clock gear train arrangement. The improved clock circuit includes the inductive winding of an electromagnetic coil, make and break contacts associated with the balance wheel armature, and the resistance of the hair spring, all serially connected to a source of direct current. A series connected reactive network, comprising a resistor-condenser combination, is connected in shunt around the make and break contact, the resistor functioning as a current limiter during the condenser discharge period and as a time delay during the recharging condenser period. denser is of substantial size so as to preclude the existence of a resonant circuit with the inductive winding of the electromagnet, and thus prevent critical circuit oscillation during the recurrent charging periods. The improved circuit also operates as a lag and damping circuit for the balance wheel and index armatures, and thereby affords a longer holding period for the index armature during each cycle of operation, after which the index armature relaxes under spring bias.

The con- In an etort to Uobviatc the irregularities caused by 2,711,501 Patented June 21, 1955 ice the applied voltage fluctuations, a low reluctance path is provided in the air gap of the magnetic circuit associated with the balance wheel armature. This object is achieved by increasing the effective area of the pole faces cooperating with the balance wheel armature such that a lower starting voltage is required to initiate and maintain balance wheel oscillation. The magnetic flux produced by the particular pole configuration disclosed, saturates the balance wheel even at minimal applied potentials. The pole pieces are accentuated in size, and incorporate wide faces for producing a concentrated ux path. The composite effect of the several improvements result in the clock which is relatively simple to adjust and extraordinarily accurate in time keeping.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. l is a bottom plan view of the clock with the back, cover and other parts removed.

Fig. 2 is a diagrammatic View showing the clock energizing circuit.

Fig. 3 iS a diagrammatic view illustrating a current condition to be avoided in the clock energizing circuit.

Fig. 4 is a diagrammatic view illustrating the current conditions existent in the clock energizing circuit of Fig. 2..

With particular reference to Fig. l, the clock includes a base plate 10 having a pair of spaced pillars 12 and 14 on which a bridge 16 is supported by screws 18. An armature 20 having three equidistantly spaced lobes, is mounted on a statt, not shown, journaled in jeweled bearings, not shown, in the bridge 16 and a portion of the base plate 1t), the armature 20 also functioning as the balance wheel of the clock. A hair spring, not shown, has its ends secured to the balance wheel stati and a portion of the base plate reSPectively, the outer turn o f the hair spring passing through a slot in a regulator arm 22 in a manner identical with that disclosed in the aforementioned copending patent. The arm 2,2 is connected in a conventional manner to a pivot post 24 which may be rotated to shorten o r lengthen the elective length of the hair spring and thereby regulate the period of oscillation of the balance wheel in a conventional manner.

The statt of the balance wheel armature 2,0 has secured thereto an electrical contact, not shown, which is connected to the base plate through the armature, staff and hair spring. The base plate in turn is grounded. The electrical contact on the balance wheel statt cooperates and is engageable with an electrical contact blade 26, one end of which is secured to a post 28 insulated from the base plate 10. The free end of the blade 26 is located so as to project into the arcuate path of movement of the contact of the balance wheel stati upon oscillation thereof. The blade 26 is suitably spring biased so that any vibrations set up in the blade 26 are rapidly damped after the deflection thereof by the balance wheel Contact.

The post 28 is electrically connected to a contact member 30. electrical conductor 32 is connected to the member 30, the conductor 32 passing through an insulating sleeve 34 within which a resistance 36 is disposed. The electrical conductor 32 connects the resistance 36 in series with one terminal of a condenser or capacitor 38 the casing of which is mounted on the base plate 10, The other terminal of the condenser 38 is electrically connected by means, not shown, to the bridge 1 6 which is electrically connected to the balance wheel armature 2Q, the stafl and the hair spring, not shown.

During normal operation .0f the Contact associated with the balance wheel staff, opposite faces of the contact 3 blade 26 are engaged thereby to facilitate intermittent energization of the winding of an electromagnet, indicated generally at 4t). Electromagnet 40 includes a core 42 having one end secured to the base plate 16 and upper and lower pole pieces 44 and 46, respectively, which are so formed as to locate the pole faces thereof in the plane Yof the armature 20 at points relatively close to the periphery thereof, in accordance with the disclosure of the aforementioned copending patent. The pole faces ofthe electromagnet are adapted to impart periodic magnetic impulses to the armature 20 to sustain the same in oscillation. One terminal of the electromagnetic winding is -electrically connected to the conductor member and the other terminal of the magnetic winding is connected to a terminal of a storage battery.

The balance wheel armature assembly, the electromagnet with its pole pieces 44 and 46, the Contact arrangement above described and the reactive network comprising the serially connected resistor condenser combination constitute a timing mechanism 'for the balance wheel armature and the electromagnetic energizing circuit. Since the mechanical load imposed upon the balance wheel armature, and friction opposing movement of the balance wheel stati is minimized and not subject to any appreciable variations, it is apparent that the balance wheel armature oscillates substantially at a frequency determined by its mass and the torque of the hair spring, as modified by the rate of flux decay in the electromagnet controlled by the aforedescribed reactive network.

Each of the pole pieces 44 and 46 is reversely bent in the medial portion thereof so that the pole faces of each pole piece lie in substantially the same plane as that of the balance wheel armature 20. The extending ends of the pole pieces 44 and 46 are respectively connected by screws 18 to pillars 12 and 14. As is readily `apparent from inspection of Fig. l, a substantial portion of the pole pieces lie in the plane of the balance wheel armature 20. The extended or accentuated pole pieces are further provided with pole face projections 48 and 50, respectively, which function to maintain a highly concentrated ux path across a portion of the armature 20.

The effective area of the pole pieces 44 and 46, which act as pole faces for the magnetic circuit of the balance wheel armature, includes the portions projecting outwardly from the bends 52 and 54 respectively thereof. That is, substantially the entire portion of the pole pieces which lie in a plane identical with that of the balance wheel armature 20, are effectively employed to saturate the balance wheel armature with magnetic flux. However, the most concentrated lines of flux will naturally exist between the projections 48 and 50. It is readily apparent that by increasing the effective area of the pole pieces associated withl the armature 20, reluctance of the airgap in the magnetic circuit may be substantially decreased. Resort is had to decrease the reluctance of the air gap to minimize erratic oscillations of the balance wheel oftentimes caused by substantial fluctuations in the voltage applied to energize the electromagnet. By employing the pole piece construction disclosed, good time keeping can be realized even though the applied voltage of theoretically six volts uctuates between 3 and 8 or morevolts. In this manner clock adjustment becomes relatively simple to accomplish.

Electromagnet also carries a pair of pole pieces adapted to actuate the index armature which drives the clock gear train. One of the additional pole pieces is indicated at 56 in Fig. 1. As this invention pertains only to the clock energizing circuit suce it to say here that the clock drive arrangement is similar to that disclosed in Patent No. 2,572,989, Contant, et al., in which intermittent energization of the electromagnet 40, as controlled by the balance wheel armature 20, imparts periodic oscillations to an index armature, not shown, mounted between the ends of the index armature pole pieces. For understanding this invention it is sufficient to say that the index armature is normally biased by a spring pawl 58, one end of which is mounted on a portion of the bridge 16 and an intermediate portion of which is tensioned by a helical spring 60. The drive pawl 58 cooperates with a ratchet wheel mounted on a shaft, not shown, carrying a worm 62 which drives the clock gear train. A holding pawl 64 is provided to insure a predetermined movement of the worm gear shaft and to prevent retrograde movement thereof during oscillation ofthe index armature.

With particular reference to Figs. 2 through 4, the clock circuit will now be described in greater detail. As is shown in Fig. 2, the clock circuit includes a source of direct current 66, one terminal of which is grounded and the other terminal of which is connected by a wire 68 to one side of the electromagnetic winding 70. The other terminal of the electromagnetic winding 70 is connected through a switch 72, which structurally comprises the Contact on the balance wheel staff and the contact blade 26, connected to one end of a resistance 74, which structurally takes the form of the balance wheel hair spring, not shown. The other terminal of the resistance 74 is connected to ground. Connected in shunt across the terminals of the make and break switch contacts 72 is a reactive network comprising the condenser 38 and the resistance 36.

For inspection of the circuit diagram shown in Fig. 2, it is apparent that when the contacts of the make and break switch 72 are open, the condenser 38 will be charged through the inductive winding 70 of the electromagnet, resistor 36, and the hair spring resistance 74. However, upon closing of the contacts of the make and break switch 72, the condenser 38 will discharge through resistance 36. Accordingly, the resistance 36 is employed as a current limiter upon capacitor discharge to limit the current owing in the intermittently short circuited capacitor circuit and prevent welding of the closed contacts of the make and break switch 72. The resistance 36 also functions as a time delay for releasing the index armature slowly upon opening of the contacts of the make and break switch 72 by retarding the recharging time of the condenser 38 through combined resistances 36 and 74 and the inductive windings 70. Thus erratic oscillations of the index armature which drives the clock gear train are effectively prevented.

Preferably the condenser 38 has a capacity within the range of to 300 microfarads. A condenser of this size is required to prevent the occurrence of critical oscillations in the energizing circuit upon recharging of the condenser. Thus, as is shown in Fig. 3, if a condenser employed is of such a value, less than 170 microfarads, as to form a series resonant circuit of the inductive winding 70 during the recharging period, critical oscillations, as indicated by the current wave form in the range X of Fig. 3, will occur. Accordingly, a condenser of substantial size is employed to preclude the existence of a resonant series circuit at the frequency of intermittent magnet energization, and produce a current wave form of the character shown in Fig. 4.

As aforementioned, charging of the condenser through the resistance and inductive winding provides a time delay for the magnetic circuit associated with the index armature, without which the return stroke of the index armature under spring bias, would be fast enough to follow the current in voltage peaks generated by critical oscillation as indicated in Fig. 3. If critical oscillations exist in the circuit during charging of the condenser employing a clock drive disclosed in the aforementioned patent, the current and voltage peaks will move the index armature more than the single armature stroke required for each closing of the contacts of make and break switch 72. The time delay effected by the reactive network in the instant clock circuit results in magnetically damping the index armature thereby resulting in more accurate time keeping.

"lhe time delay effected by the condenser-resistor comarticoli bination in shunt with the switch 72 also functions to retard the rate of flux decay of the electromagnetic circuit associated with the balance wheel armature 20. In essence, this retarded rate of flux decay functions as a magnetic drag or damping of the balance wheel, and results in a substantially constant balance wheel amplitude of movement regardless of vibrations normally encountered by clocks installed in automobiles. Automobile vibration ordinarily results in an increase of balance wheel movement which tends to disrupt the harmonic balance wheel motion required for accurate time keeping. By employing a clock circuit of the type herein disclosed, the time delay produced by the resistorcondenser combination tends to maintain harmonic motion of the balance wheel in spite of extraneous vibrations.

In operation, harmonic movement of the balance wheel armature will effect intermittent energization of the electromagnetic winding 70 which, :in turn, effects movement of the index armature that drives the clock gear train. The reactive network employed in the energizing clock circuit provides a time delay which retards the rate of flux decay in the magnetic circuits associated with both the balance wheel armature 20 and the index armature, not shown. Moreover, by employing pole pieces having accentuated face areas in the magnetic circuit of the balance wheel armature 20, normal voltage fluctuations encountered in automobile use will have no effect on the accuracy of time keeping.

From the aforegoing .it is apparent that the present invention provides a clock control circuit facilitating the production of an impulse type clock in mass quantities without resort to individual adjustment of each clock assembly. Moreover the improved clock construction results in a clock which is relatively simple to produce and very reliable in time keeping over a wide variation in the potential applied voltage.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

l. In an electric clock of the magnetic impulse type which is subjected to mechanical vibrations, an electromagnet having a magnetizing winding and a pair of pole pieces having accentuated pole faces, a balance wheel armature mounted for substantially constant amplitude oscillation between said pole faces, said pole pieces and armature constituting a low reluctance magnetic circuit that saturates the armature with ux a circuit operable to periodically energize the winding including coacting contact members controlled by the motion of the balance wheel armature and actuated thereby during each cycle of armature oscillation, and a time delay reactive network shunting said coacting contact members to retard the rate of tlux decay in said pole pieces upon opening of said contact members whereby harmonic motion of the balance wheel armature may be maintained irrespective of mechanical vibrations.

2. In an electric clock of the magnetic impulse type, an electromagnet having an inductive winding and a pair of pole pieces having accentuated pole faces, a balance wheel armature mounted for oscillation between said pole faces, a circuit operable to periodically energize the winding including coacting contact members controlled by the motion of the balance wheel armature, and a serially connected resistor-condenser combination shunting said coacting contact members to retard the rate of flux decay in said pole pieces upon opening of said contact members, said condenser being of a sufficient capacity to prevent the establishment of a series resonant circuit with the inductive winding of said electromagnet when said contact members are separated.

3. In an electric clock of the magnetic impulse type, an electromagnet having a magnetizing winding and a pair of opposed pole pieces having pole faces disposed in the plane of an oscillatable balance wheel, each pole face having a substantial portion thereof disposed in contiguous relation to the periphery of the balance wheel and having a projection thereon extending towards the axis of the balance wheel so as to provide a low reluctance magnetic circuit having a path of concentrated flux, a circuit operable to periodically energize the winding including a source of current and coacting contact members controlled by the motion of the balance wheel, the magnetic circuit being such that the pole faces of said electromagnet saturate the balance wheel with magnetic ux during variations in the applied potential of said source of current over a substantial range and thereby maintain substantially constant amplitude oscillation of said balance wheel.

4. In an electric clock of the magnetic impulse type, an electromagnet having a magnetizing winding and a pair of opposed pole pieces having pole faces disposed in the plane of an oscillatable balance wheel, each pole face having a substantial portion thereof disposed in contiguous relation to the periphery of the balance wheel and having a projection thereon extending towards the axis of the balance wheel so as to provide a low reluctance magnetic circuit having a path of concentrated ux, a circuit operable to periodically energize the winding including a source of current and coacting contact members controlled by the motion of the balance wheel, the magnetic circuit being such that the pole faces of said electromagnet saturate the balance wheel with magnetic flux during variations in the applied potential of said source of current over a substantial range, and a time delay reactive network shunting the coacting contact members to retard the rate of ux decay in said pole faces upon opening of said contact members.

5. In combination with an electric clock of the magnetic impulse type, an electromagnet having a winding and a pair of pole pieces having accentuated pole faces, a balance wheel armature mounted for substantially constant amplitude oscillation between said pole faces, a source of direct current, circuit connections between said source and said winding including a periodically actuated make and break switch operatively associated with said balance wheel and actuated during each cycle of balance wheel oscillation, and a time delay reactive network shunting said make and break switch to control the rate of flux decay in the electromagnet upon opening of the make and break switch.

6. The combination set forth in claim 5 wherein the time delay reactive network comprises a serially con` nected condenser-resistor combination, the condenser being of such capacity as to prevent the establishment of a series resonant circuit with said electromagnet winding when the make and break switch is open.

7. In an electric clock of the magnetic impulse type, an electromagnet having an inductive winding and a pair of pole pieces having pole faces disposed in the plane of au oscillatable balance wheel, each pole face having a substantial portion thereof disposed in contiguous relation to the periphery of the balance wheel and having a projection thereon extending toward the axis of the balance wheel so as to form a low reluctance magnetic circuit having a path of concentrated flux, a circuit operable to periodically energize the inductive winding including a source of current and coacting contact members controlled by the motion of the balance wheel and actuated during each cycle of balance wheel dscillatiom the magnetic circuit being such that the pole faces of said electromagnet saturate the balance wheel with magnetic ux irrespective of substantial variations in the applied potential of said source of current, and a damping circuit operable to retard the rate of ux decay upon deenergization of said inductive winding, said damping circuit including a serially connected condenser resistor combination shunting said coacting contact members, said condenser having a capacity sutii- .7 cient to prevent the establishment of a series resonant 2,153,775 circuit with said inductive Winding when said ooacting 2,183,062 contact members are separated. Y 2,357,645 2,623,699 References Cited in the le of this patent 5 2,631,423

UNITED STATES PATENTS 1,978,311 Julian Oct. 23, 1934 8 Poole Apr. 11, 1.939 Conrad Dec. 12, 1939 Gibbs et al. Sept. 5, 1944 Smith Dec. 30, 1952 Sullivan et al. Mar. 17, 1953 

